Atherosclerosis occurs when plaque and scar tissue build up, causing the arteries to narrow.

As PAD progresses, blood flow is restricted (as shown on the right leg) to the lower limbs, causing pain.

Peripheral arterial disease affects more than 30 million people worldwide, and while it can strike anyone, it's most common in people over age 65.

PAD develops most often as a result of the hardening of arteries (atherosclerosis), which occurs when cholesterol levels and/or scar tissue build up, causing the arteries to narrow and restrict blood flow.

Millions affected
According to the Society of Interventional Radiology, people over age 50 who smoke or have diabetes are at increased risk of developing PAD, as are African Americans. Overall, it is estimated that up to 20 percent of all adults over age 65 are affected by PAD - or as many as 30 million people.

Missed diagnoses
PAD is seriously under-diagnosed and under-treated. According to scientific reports, many people with PAD do not exhibit warning signs of the disease. In fact, of those who have been diagnosed with PAD, only 33 percent exhibited any symptoms. Those who do have severe symptoms often simply attribute them to advanced age.

Untreated, PAD can lead to difficulty in walking and, in its most severe stage, gangrene leading to leg amputation. Also, people who have PAD often have arterial blockages in other parts of the body and are, therefore, at greater risk of suffering a heart attack or stroke.

Common symptoms
The most common symptom of PAD is leg pain that occurs when walking but disappears during rest. Other symptoms include:

Risk factors
Since PAD is similar to cardiovascular disease - which causes blocked arteries - the risk factors of PAD are similar to the risk factors of heart disease.

The most common risk factor is smoking. The American Heart Association says that, on average, smokers are diagnosed with PAD 10 years earlier than nonsmokers.

Diabetes is also a leading risk factor for PAD; people with Type 2 diabetes have three to four times the normal risk for PAD.

Other risk factors include:

Common questions about peripheral arterial disease:

Q. What causes PAD?

A. PAD develops most often as a result of the hardening of arteries (atherosclerosis), which occurs when cholesterol levels and/or scar tissue build up, causing the arteries to narrow and restrict blood flow.

Q. How is PAD diagnosed?

A. Unfortunately, many cases of PAD go undiagnosed because the symptoms are often mistaken for the effects of advanced age. An ankle-brachial test (ABI) is one way to determine whether someone could be suffering from PAD. The ABI test measures the blood pressure at the ankle and at the arm. A comparison of the two blood pressure readings can point to problems. Specifically, a blood pressure that is lower in the ankle than in the arm implies a blockage in the artery between the heart and the leg. Other tests used to diagnose PAD include ultrasounds, X-rays, angiography and magnetic resonance imaging angiography (MRA).

Q. What is the most common treatment for PAD?

A. Lifestyle changes - such as smoking cessation, exercise, lowering blood pressure and cholesterol - can help to change the progression of PAD and decrease the likelihood of a heart attack or stroke. Lifestyle changes often are made in combination with the use of certain drugs - such as antiplatelet therapy, statins and ACE inhibitors - that help to reduce cholesterol levels and blood pressure.

Q. What are the treatment options for patients who do not respond to lifestyle changes or drug therapy?

A. PAD can be treated with angioplasty, a non-surgical procedure that widens narrowed or blocked peripheral arteries. In this procedure, a catheter with a deflated balloon is inserted into the narrowed artery segment. The balloon is inflated to force open the artery, and then the catheter is deflated and withdrawn. Angioplasty also can be combined with a stent, a metal device that acts like a scaffold and remains in the artery after the catheter is withdrawn to keep the vessel open. Another option is bypass surgery, which involves attaching a vein from another part of the body or a fabricated blood vessel above and below a blocked area to detour blood flow around the blockage. Clinical trials are currently underway to test the safety of minimally invasive surgery with a drug-coated stent, which holds open narrowed arteries and is believed to prevent the arteries from narrowing over time.

Q. What can I do to reduce leg pain associated with PAD?

A. Pain is caused when the leg muscles do not receive the oxygen-rich blood required during exercise. With PAD, this pain can be severe enough to keep a person from walking. Although antiplatelets, such as aspirin, ACE inhibitors and statins, can help to reduce blood pressure and cholesterol levels and thus slow the progression of PAD, leg pain might require other treatments. Quitting smoking and beginning an exercise program can help, but people suffering from leg pain also can take FDA-approved drugs to reduce their pain.

Q. If I quit smoking, will that cut my risk for developing PAD?

A. Studies have shown that people who quit smoking can slow the progression of PAD as well as other vascular diseases.

Q. Does PAD affect men more than women?

A. According to the Society of Interventional Radiology, men typically exhibit symptoms of PAD earlier in life than women. Men are more likely to experience the onset of PAD symptoms in their 50s; symptoms typically first affect women in their 60s.

Q. What is the risk of PAD in people over the age of 65?

A. Studies show that the risk of developing PAD increases with age. Data reveal that up to 20 percent of people over the age of 65 develop PAD.

Q. How can I manage my risks of developing PAD?

A. Since smoking is the number one risk factor for developing PAD, smoking cessation can decrease the likelihood of developing the disease. In fact, according to the American Heart Association, smokers are up to 25 times more likely to develop PAD than non-smokers.

Also, people can reduce their risks for developing PAD by:

Q. What new treatments are in development for PAD?

A. A landmark trial is underway, which will include several clinical trial sites in the United States and several sites in Europe, Asia, Latin America, Australia and Canada to test the safety and effectiveness of a drug-coated stent for the treatment of PAD. This is the first time a vascular stent coated with the drug paclitaxel is being tested outside the heart. The study ultimately will determine whether the stent is successful in opening arteries in the leg and keeping them open over time.